Rolling mill control

ABSTRACT

This disclosure relates to a control for a rolling mill in which a signal representing the required stretch of the mill for a desired thickness of product and roll gap setting, which stretch is first employed to set the initial roll gap predicated on a predicted rolling pressure, is compared with a signal representing the actual stretch of the mill during rolling. A third signal is produced representing the difference between the first and second signals and which equal the amount which the product differs from the desired gage due to improper initial estimate of predicted rolling pressure employed to set the initial roll gap and, consequently, the required change that must be made to the roll gap to produce a product of the given thickness.

United States Patent [191 Adair et al.

1 ROLLING MILL CONTROL [75] Inventors: James Richard Adair; Ronald Wesley Deems, both of Pittsburgh,

[73] Assignee: Wean United, Inc., Pittsburgh, Pa.

221 Filed: ""octf'ififii 21 Appl. N0.: 187,253

[52] US. Cl. 72/8, 72/20 [51] Int. Cl B2lb 37/12 [58] Field of Search 72/8, 17, 20, 21

[56] References Cited UNITED STATES PATENTS 3,269,160 8/1966 Halter et al..... 72/8 3,496,743 2/1970 Stone 72/8 3,253,438 5/1966 Stringer 72/12 3,574,279 4/1971 Smith, Jr 72/7 3,574,280 4/1971 Smith, Jr 72/8 3,568,637 3/1971 Smith, Jr 72/8 3,592,030 7/1971 Smith, Jr 72/8 MOTOR POSITION CONTROL 1 Oct. 23, 1973 3,625,037 12/1971 Michel 72/8 Primary Examiner-Milton S. Mehr Attorney-Henry C. Westin [57] ABSTRACT initial estimate of predicted rolling pressure employed to set the initial roll gap and, consequently, the required change that must be made to the roll gap to produce a product of the given thickness. 7

3 Claims, 1 Drawing Figure l. DESIRED GAGE T 2. ROLL GAP I Go 3. REQUIRED HILL STRETCH PAIENIEB m 23 um tuhuthw 4: 00250! n 401F200 ZOPZMOL INVENTORS JAMES R. ADAIR RONALD W. DEEMS HENRY C. WESTIN ATTORNEY 1 ROLLING MILL CONTROL Rolling mill controls generally are concerned with effecting a change in the roll setting as a function of a change in the rolling pressure. Prior patents that, at least in part, envision such a control are U. S. Pat. No. 2,726,541 that issued to R. B. Sims on Dec. 13, 1955 and No. 3,496,743 that issued to M. D. Stone on Feb. 24, 1970. In the general practice of such controls, the initial roll setting or roll gap is selected before the product is received by the mill. This setting can be determined by a computer, from empirical data or from a calculated rolling schedule. Since, however, the rolling pressure does not bear a consistent relationship with the reduction necessary to yield the desired thickness, the initial setting of the roll opening may be and, actually, in many cases is incorrect. This usually is a result of using an incorrect estimate of the stretch of the mill for a desired thickness to be produced which results in an error in thickness of the workpiece being rolled.

Such thickness errors are not generally compensated for by the gauge control system of the types noted above since these systems lock on to the initial rolling load (or mill stretch) at the front end of the product and are only concerned with compensating for changes in the stretch caused by a change in the rolling pressure during rolling, the object of which beingto produce uniform gauge along'the length of the product and only after the initial establishment of a rolling pressure. The thickness at the beginning of the lock on is governed by the rolling pressure at that time, which may be different than the conditions for which the roll gap was originally set. For example, locking on Over a chilled skid mark, a tapered front end, or a colder than normal portion would result in an erroneous mill stretch with reference to the mill stretch for normal reduction.

It is, therefore, one of the objects of the present invention to provide in a rolling mill control means for producing a representation of the precise amount of difference between a predicted or required mill stretch for a given rolling pressure and the actual stretch of the mill for the given or a different rolling pressure.

It is a further object of the present invention to provide a control for a rolling mill having a roll gap, including means for producing a first signal representing the required stretch of the mill relative to a desired thickness of product to be rolled, means for setting the initial no-load roll gap to equal .the desired thickness to be rolled less the required mill stretch to obtain that thickness, means for producing a second signal representing the actual stretch of the mill during rolling, means for producing a third signal derived from a comparison of said first and second signals and which represents the amount of error in the product thickness at the existing rolling pressure, and means for employing said third signal to change the roll gap to produce a product of said desired thickness.

These objects, as well as other features and advantages of the present invention, will become better understood when the following description is read along with the accompanying drawing, which illustrates in schematic form a control system employing the features of the present invention.

In referring to the drawing, there is shown in outline form one of two upright housings 9 having a vertical elongated window 10 into which there is received a pair of cooperating work rolls 11 and 12, each of which are backed up by back-up rolls 13 and 14, respectively, in a customary manner. The bearing chock assemblies for the back-up rolls l3 and 14 are shown received in the window and are adapted to slide vertically therein relativeto the housing according to the construction of well-known practice. The upper back-up roll bearing chock assembly 18 is engaged by a mill screw 21 which is driven by a worm-wheel set 22, the worm of which is shown diagrammatically to be driven by an electrical motor 23 and through the operation of which the initial gap between the work rolls 1 1 and 12 is set. This initial roll gap setting is accomplished through a position control 24 which is electrically connected to the motor 23.

With reference to the bearing chock assembly 19 of the lower back-up roll 14, it is adapted to be moved vertically by an hydraulic piston cylinder assembly 27, the piston of which is identified as 27a and the cylinder as 27b, it being noted that in the illustrated construction the cylinder 27b engages the lower surface of the back-up chock assembly 19 and moves relative to the stationary piston 27a. In accordance with well-known practice and as illustrated in the aforesaid Stone US. Pat. No. 3,496,743, there is associated with the piston cylinder assembly 27 a pair of position indicators 28 which measure the movement or displacement of different mill parts, for example, the cylinder 27b relative to the position 27a as a function of a change in the roll gap between the work rolls 11 and 12. It will be appreciated that many of the aforesaid components will be provided in the other housing of the mill and, particularly, the cylinder assembly and position indicator, as well as a screwdown mechanism. As noted, all of the aforesaid elements are well known in the rolling mill art and particularly the cylinder assembly and position indicator arrangement, the construction and function of which is set forth more specifically in the aforesaid US. Pat. No. 3,496,743.

The piston cylinder assembly 27 is controlled by a servo-valve 29 which, in turn, is controlled by a gap control system set forth within the outline block identified as 31. The gap control system 31 follows the gap control system set forth in the aforesaid U.S. Patent No. 3,496,743. Very briefly, it includes in a simplified form an amplifier 32 that feeds a signal representing the amount of difference either betweenthe actual stretch and required or a change therebetween which is represented as AP/M in the drawing. The amplifier 32 produces a signal that operates the servo 29to move the cylinder 27b either up or down, depending on whether the correction to the roll gap requires an opening or closing thereof. The servo 29 will continue to operate the pistoncylinder assembly 27 in the'required direction until a feedback signal, which is sent to a summing amplifier 33, indicates that the amount of movement of the cylinder equals the stretch error signal of the mill as represented by the signal issuing from the amplifier 32. In accordance with the aforesaid Stonev US. patent, this feedback signal is represented by a load cell signal, shown in the drawing as a Q signal, which is combined with a signal representing the modulus of a spring associated with the load cell to produce a signal Q/M, where I Q the force of the load cell M, the modulus of the spring. The signal from the position indicator 28, represented on the drawing as a Q value, is first sent to an amplifier 35 to produce a signal representing the initial, reading of the position indicator, as represented by a value Q lM, Once this signal is produced, it is held in a memory circuit 36 and employed as a reference value and compared with any change in the Q signal coming from the position indicator 28 as a result of a change in the rolling pressure of the mill. The signal coming from the position indicator 28 is sent also to an amplifier 37 to which there is fed a signal representing the modulus of the spring M, through a line 38 whereby the amplifier 37 produces a value representing Q/M, which is the actual stretch of the cell and spring system, which signal is sent to a summing amplifier 39 where the actual stretch of the spring and load cell is compared with the reference signal Q /M. to produce a signal representing the change in the stretch of the load cell and spring of the position indicator 28. This operation produces the feedback signal represented by AQ/M, which is fed to the summing amplifier 33. As noted before, in the summing amplifier 33 the stretch error signal of the mill as represented by a signal produced by the amplifier 32 and identified as AP/M is substracted from the signal AQ/M, until the difference equals zero. When this occurs, there will be an interruption of the operation of the servo 29 indicating that the necessary amount of correction has been made with reference to the stretch condition of the mill.

In still referring to present-day rolling mill practice, as observed before, it is the present practice with reference to establishing the amount of change of the stretch of the mill to compare the actual stretch with a reference value. The manner of developing this reference value is summarily illustrated in a subcontrol circuit 41. In the customary manner, there is provided be tween the backup chock 18 of the upper backup roll 13 a load cell 42- which produces a continuous signal proportional to the rolling load, which is fed in part to the circuit 41 and, more particularly, to an amplifier 43 in the form of a signal P, The amplifier also receives a signal representing the modulus of the mill identified as M,, through a line 44. By means of a memory unit 45 the initial stretch of the mill, represented by the value P /M is recorded and a signal thereof is sent to the amplifier 32. t

The signal Prepresenting the rolling load is also sent to a second subcontrolcircuit 48 which includes an amplifier 49 to whichis also fed an additional signal representing the modulus of the mill M through line 51, which may be adjustable to suit differentoperating mill conditions. Accordingly, the amplifier 49 produces a signal representing the actual stretch of the mill, which signal is sent from the amplifier 49 to the amplifier 32 where it is compared with the. initial signal of the stretch of the mill as produced by the circuit 41 and from which comparison there is produced the amount of change in the mill. stretch represented by a value AP/M the electrical signal representing this being produced and sent by the amplifier 32 'to the amplifier 33. As noted previously, the inability prior to the present invention toestimate initially and, accordingly, set the initial gap with reference to the exact amount of stretch of the mill for a given product thickness resulted in an error in the initial reference modulus in the subcontrol circuit 41. Such reference errors in previous and present-day control arrangements have been used and compared with the acutal stretch of the mill so that the amount of required roll gap change produced by this comparison has inherently incorporated the error initially involved in the setting of the no-load roll gap.

It is an object of the present invention to eliminate this error and to produce a signal representing the exact amount of stretch of the mill and, more particu larly, a signal representing the amount of difference between the predicted and actual stretch of the mill. The present invention eliminates altogether the circuit and function of the circuit41 and provides instead through a control unit 53 the generation of an electrical signal over a line 54 representing the required or predicted stretch of the mill for a desired thickness, which signal, as illustrated in the drawing, is sent to the summing amplifier 32 where it is compared with the actual stretch of the mill as produced by the amplifier 49. The generating signal representing the required mill stretch for a given thickness of product may be developed by a card system of the type well known in rolling mill practice, in which the data on the card being fed to a computer is arrived at through an empirical examination of previous rolling conditions with respect to the type, temperature, thickness, etc. of the product to be rolled. Such a signal representing the required mill stretch can also be produced continuously through a computer working in conjunction with known means for examiningthe various parameters that make up the stretch of the mill, which means can be associated with the mill in such a way as to examine the product while it is being rolled. In addition to the signal generated through the line 54,

the control unit 53 sends a signal over line 55 to the po-' sition control 24 to set the initial no-load roll gap of the mill. The amount of no-load roll opening between the work rolls 11 and 12, as set by the control 24, will follow the equation:

T G0 S where T the desired gauge Go the no-load roll gap setting S predicted mill stretch I In describing one form of employing the rolling mill control herein described, the roll gap will beset before rolling commences by a signal from the control unit 53,

actual stretch of the mill. This signal is then'compared in the amplifier 32 with the predicted stretch of the mill as established by the control unit 53 and fed by line 54 to the amplifier 32. Should there be any difference between the two signals, for example, as on the change of the rolling pressure, the amplifier 32 will produce a sig nal representing the amount of error in the predicted thickness at the existing rolling pressure, which signal will be sent to the amplifier 33 to operate the servovalve 29 to correct the roll gap to reduce the error to;

zero. Thissignal from the amplifier 32 will'be characterized by either a positive or negative value 'so that the signal going to the servo 20 will effect an increase or decrease in the roll gap of the mill by an amount equal to the difference between the predicted and actual stretch of the mill caused by the change in the rolling pressure thereof.

In accordance with the provisions of the patent statutes, we have explained the principle and operation of our invention and have illustrated and described what we consider to represent the best embodiment thereof.

We claim: I

1. In a control for a rolling mill for rolling to an absolute desired thickness from the earliest developed rolling pressure of said mill, said mill having a roll gap, and said control including means for producing prior to rolling a first signal representing an absolute selected anticipated value of the stretch of the mill for a selected reduction of a given rolled product,

the' value of said first signal remaining constant throughout the entire rolling operation of said given rolled product, means for setting said roll gap so that the sum of said roll gap setting and said value of said first signal will equal the absolute thickness of the rolled product,

means for producing a second signal representing the actual stretch of said mill during rolling,

means for comparing said first and second signals and producing a third signal representing the amount of any deviation of the actual mill stretch from the absolute selected anticipated value of the mill stretch, and

means for receiving said third signal and for effecting a change in the roll gap to offset the stretch difference to produce a product of said absolute thickness.

2. In a rolling mill according to claim 1, including means for producing a signal representing the initial roll gap, which signal equals the desired thickness less the desired mill stretch.

3. In a rolling mill according to claim 2, including a mechanical means for receiving said initial roll gap signal and for setting said initial roll gap and wherein said means for receiving said third signal includes a piston cylinder assembly. 

1. In a control for a rolling mill for rolling to an absolute desired thickness from the earliest developed rolling pressure of said mill, said mill having a roll gap, and said control including means for producing prior to rolling a first signal representing an absolute selected anticipated value of the stretch of the mill for a selected reduction of a given rolled product, the value of said first signal remaining constant throughout the entire rolling operation of said given rolled product, means for setting said roll gap so that the sum of said roll gap setting and said value of said first signal will equal the absolute thickness of the rolled product, means for producing a second signal representing the actual stretch of said mill during rolling, means for comparing said first and second signals and producing a third signal representing the amount of any deviation of the actual mill stretch from the absolute selected anticipated value of the mill stretch, and means for receiving said third signal and for effecting a change in the roll gap to offset the stretch difference to produce a product of said absolute thickness.
 2. In a rolling mill according to claim 1, including means for producing a signal representing the initial roll gap, which signal equals the desired thickness less the desired mill stretch.
 3. In a rolling mill according to claim 2, including a mechanical means for receiving said initial roll gap signal and for setting said initial roll gap and wherein said means for receiving said third signal includes a piston cylinder assembly. 